OBJECTIVE: To correlate androgen and adrenal excretion in male tamarins along with behavioral measurements of development. To compare both hormonal and behavioral development of male tamarins with adult breeding males in families and with adult males recently paired with females. RESULTS Functional changes in DHT levels correlated with morphological changes in male sexual development whereas testosterone levels did not. Cortisol increases were associated with changes in social environment but testosterone levels did not change with social or sexual stimulus. We have followed natal males with urine collection to create hormonal profiles from infancy through adulthood. Hormonal profiles for T and DHT were summarized for the natal males. Preliminary analyses of DHT profiles showed that DHT rather than T is more indicative of the pubertal and maturation processes in tamarin males. Males showed an increase in urinary DHT levels at approximately 40 weeks of age, which increased further through two years of age. For the two males who represented ages below 15 wks, post-natal levels of T and DHT appeared to nadir at 15 to 20 weeks of age. Patterns of hormones and behavior are being summarized for males living in natal groups immediately before and after pairing to see if males display inhibition of sex steroids or sexual behavior that is altered when social environments are altered. We have validated our non-invasive scrotal measurement technique with conventional caliper measurements. FUTURE DIRECTIONS We plan to continue examining hormonal and behavioral development of male tamarins. KEY WORDS testosterone, cortisol, DHT, sexual development, social development, New World primates Ziegler, T.E., A.A. Carlson, and C.T. Snowdon. 1997. Testosterone excretion into the urine of male cotton-top tamarin monkeys Saguinus oedipus and the source of urinary oestrogens. Journal of Reproduction and Fertility. [J]